Hydro-forming of steel and other metal hollow members is becoming increasingly common. With hydro-forming the cost of manufacture of hollow members can be reduced, in comparison to conventional stamping, welding and other manufacturing techniques. Further, the quality (strength, tolerances, etc.) of the finished hydro-formed member can exceed the quality of members formed with conventional techniques.
After a member has been hydro-formed, it typically requires a series of additional manufacturing operations and/or forming steps. One common post-forming operation is the need to form one or more apertures in the member and much effort has previously been devoted to forming these apertures in the member via piercing when the formed member is still in the hydro-forming die.
While piercing is now commonly used to form desired apertures in hydro-formed members, difficulties still exist with piercing technologies. In particular, the size of the cylinders required to perform the pierce can restrict the number of apertures that can be formed in any region of the member, as insufficient volume may be available to accommodate the cylinders in the region of interest. Further, the quality (shape and/or clean cut of the edges) of the aperture may not be as good as desired.
To address these issues, piercing systems which employ a negative pierce have been proposed. In the proposed negative pierce system, the piercing punch is retracted during a portion of the hydro-forming cycle such that the portion of the formed member to be pierced is extruded outward from the formed member. The piercing punch is then extended into the extruded portion to pierce the resulting weakened area and form the desired aperture. By first extruding the portion to be pierced, the force required to perform the pierce is reduced, allowing for a smaller cylinder to be employed for a given sized aperture and allowing for a better quality aperture to be obtained.
While the proposed negative pierce operations provide advantages, the additional complexity and expense required to operate the hydraulic cylinder to first retract and then extend the piercing die increases the expense of the hydro-forming set up. Further, the extra complexity (hydraulic lines, stops, etc.) can occupy more volume in the hydro-forming die, thus limiting the number of apertures and/or spacing of those apertures that can be formed in a given area of the hydro-formed member.
It is desired to have a piercing device and method which provides for negative piercing while avoiding the need for complex and/or bulky hydraulic control systems.